The invention relates generally to marine engines, and more particularly, to propeller hubs.
Outboard engines include a drive shaft which extends from the engine power head, through an exhaust case, and into an engine lower unit. The lower unit includes a gear case, and a propeller shaft extends through the gear case. Forward and reverse gears couple the propeller shaft to the drive shaft. The drive shaft, gears, and propeller shaft sometimes are referred to as a drive train.
A propeller is secured to and rotates with the propeller shaft. Torque from the engine is transmitted from the propeller shaft to the propeller. Exemplary propeller hub assemblies include cross bolts, keys, shear pins, plastic hubs, and compressed rubber hubs. Such hub assemblies should have sufficient strength or stiffness so that during normal engine operations, very few losses occur between the propeller shaft and the propeller. Such hub assemblies, however, also should be resilient so that the engine drive train is protected in the event of an impact, e.g., if the propeller hits a log or rock.
A propeller hub assembly also should facilitate xe2x80x9climp homexe2x80x9d operation of the engine so that even in the event that an interface between the propeller shaft and the propeller shears due to a large impact, the propeller and propeller shaft still remain sufficiently engaged so that the engine still drives the boat, for example, to return to a dock for repairs.
In an exemplary embodiment, a propeller assembly includes a plastic bushing secured, e.g., bonded, to an inner hub and configured to engage an outer hub of a propeller. More specifically, and in an exemplary embodiment, the bushing includes a cylindrical shaped body having a bore therethrough, and a plurality of grooves are in an outer diameter surface of the cylindrical shaped body. The inner hub includes a cylindrical shaped body sized to extend into the bushing bore. A flange is at one end of the inner hub body, and at least one limp home tab extends from the flange.
The propeller includes an outer hub having a cylindrical shaped body, and a plurality of blades extend from an outer diameter surface of the outer hub body. An inner diameter surface of the outer hub body has a plurality of protrusions that extend radially inward. Each protrusion is positioned to extend within a respective one of the grooves in the outer diameter surface of the bushing body. Also, at least one limp home tab extends from the outer hub inner diameter surface.
Generally, the propeller assembly rotates with the propeller shaft during normal operations. In the event of an impact, e.g., the propeller strikes an object in the water, the propeller may rotate relative to the shaft. Specifically, in the exemplary embodiment, since the torsion bushing is plastic and outer hub is stainless steel, the outer hub may rotate relative to the bushing.
In the event that such relative rotation of the propeller results in shearing the engagement between the propeller and the torsion bushing, a limp home arrangement provides that the propeller may still be rotatable with the propeller shaft so that the operator can at least reach a dock for repairs. The limp home arrangement includes the outer hub tabs and the inner hub tabs. Once the propeller outer hub rotates so that the outer hub tabs engage the inner hub tabs, the outer hub once again rotates with the propeller shaft. Such operational condition is sometimes referred to herein as the limp home operation mode.